1. Field of the Invention
This invention relates to an electrical connecting member for use when electric circuit parts are to be electrically connected together and a method of manufacturing the same.
2. Related Background Art
As methods of electrically connecting electric circuit parts together, there are known the wire bonding method and the TAB (tape automated bonding) method. However, these methods have suffered from the difficulties that they cannot cope with an increase in the number of connection points between electric circuit parts and that they are costly. In order to overcome such difficulties, it is known to electrically connect electric circuit parts together by the use of an electrical connecting member of a construction having a plurality of electrically conductive members provided in a mutually insulated state in an insulative holding member (Japanese Laid-Open Patent Application No. 63-222437, Japanese Laid-Open Patent Application No. 63-224235, etc.).
FIG. 1 of the accompanying drawings is a schematic view showing the electrical connection of electric circuit parts using such an electrical connecting member. In FIG. 1, the reference numeral 31 designates an electrical connecting member, and the reference numerals 32 and 33 denote electric circuit parts to be connected together. The electrical connecting member 31 comprises a plurality of electrically conductive members 34 formed of a metal or an alloy, electrically insulated from one another and provided in a holding member 35 formed of an electrically insulative material, and one end 38 of each electrically conductive member 34 is exposed on the side of one electric circuit part 32 and the other end 39 of each electrically conductive member 34 is exposed on the side of the other electric circuit part 33 (FIG. 1(a)). The connecting portion 36 of said one electric circuit part 32 and one end 38 of each electrically conductive member 34 exposed on the side of the electric circuit part 32 are made into an alloy to thereby join the two together, and the connecting portion 37 of said other electric circuit part 33 and the other end 39 of each electrically conductive member 34 exposed on the side of the electric circuit part 33 are made into an alloy to thereby join the two together and thus, the electric circuit parts 32 and 33 are electrically connected together (FIG. 1B).
Such an electrical connecting member has the following advantages:
(1) By making the size of the electrically conductive members minute, the connecting portions of electric circuit parts can be made small and therefore, the number of connection points can be increased and consequently, denser connection of the electric circuit parts is possible. PA1 (2) Even in the case of electric circuit parts differing in thickness from each other, it becomes possible to make the height of the electric circuit parts always constant by changing the thickness of the electrical connecting member and thus, multilayer connection can be easily accomplished and denser mounting is possible. PA1 (3) By making the height of protrusion of . electrically conductive members connected to the connecting portions of electric circuit parts great, it becomes possible to accomplish stable connection even if the connecting portions of the electric circuit parts are depressed from the surface thereof, and it is possible to easily connect even electric circuit parts of complicated shape together.
A method of manufacturing the above-described electrical connecting member for effecting the electric multipoint connection of electric circuit parts is proposed in Japanese Laid-Open Patent Application No. 2-49385. This method will hereinafter be briefly described with reference to FIG. 2 of the accompanying drawings which schematically shows the steps thereof.
A base body 51 comprising a metal sheet such a copper plate is first prepared, and negative-type photosensitive resin 52 is applied onto this base body 51 by a spin coater, and pre-baking is effected at a temperature of about 100.degree. C. (FIG. 2A). Light is applied to the photosensitive resin 52 through a photomask (not shown) forming a predetermined pattern, whereafter developing liquid is injected to the photosensitive resin or the photosensitive resin is immersed in developing liquid to thereby effect development. The photosensitive resin 52 remains on the portions exposed to light and the photosensitive resin 52 is removed from the portions not exposed to light by the developing process, whereby a plurality of apertures 53 are formed (FIG. 2B). Temperature is increased to 200.degree.-400.degree. C. to cure the photosensitive resin 52, whereafter etching is effected with the base body 51 immersed in etching liquid, whereby recesses 54 communicating with the apertures 53 are formed in the base body 51 (FIG. 2C). Gold plating is then applied with the base body 51 as a common electrode to thereby fill the apertures 53 and recesses 54 with gold 55, and gold plating is continued until bumps are formed (FIG. 2D). Finally the base body 51 is removed by etching, whereby there is manufacture an electrical connecting member 31 (FIG. 2E).
FIG. 3 of the accompanying drawings is a schematic view showing the state of the electroplating step in such a process. In FIG. 3, the reference numeral 61 designates a plating vessel. A mesh-like anode 62 is disposed in the lower portion of the plating vessel 61, and a cathode 63 is disposed in the upper portion of the plating vessel in opposed relationship with the anode 62. An intermediate member 64 as shown in FIG. 2C is placed on the cathode 63, and plating liquid 65 low in gold concentration is caused to flow at a low speed from below toward above to thereby apply so-called strike plating and coat the surfaces of the recesses 54 with gold, whereafter so-called thickening plating is applied by the use of plating liquid high in gold concentration to thereby fill the recesses 54 and apertures 53 with gold, thus forming electrically conductive members 34.
In the electrical connecting member 31 manufactured in this manner, the gold 55 constitutes the electrically conductive members 34 and the photosensitive resin 52 constitutes the holding member 35. As regards the dimensions of respective portions of the electrical connecting member 31, the thickness of the photosensitive resin 52 (the holding member 35) is about 10 .mu.m, the diameter and pitch of the apertures 53 (the electrically conductive members 34) are about 20 .mu.m and about 40 .mu.m, respectively, and the amounts of protrusion of the electrically conductive members 34 on the obverse and reverse are of the order of several .mu.m.
The reliability of the above-described electrical connecting member is achieved by bumps of a uniform shape and uniform height of protrusion being provided.
However, the conventional developing step and the subsequent gold electroplating step have suffered from the following problems.
First, in the developing step, due to the developing liquid infiltrated in the photosensitive resin 52, the photosensitive resin 52 becomes liable to flow with the developing liquid or dissolve in the process of leaving the photosensitive resin 52 as it is after the developing step or in the process of curing the photosensitive resin 52 after the developing step. Accordingly, as shown in FIG. 4 of the accompanying drawings which shows the state before the formation of the recesses 54 on an enlarged scale, the formed apertures 53 are tapered at 53a or the pattern thereof gets out of shape, and the shape of the apertures 53 becomes irregular. This leads to the problem that in the manufactured electrical connecting member 31, the shape of the electrically conductive members is not stable.
There is further a problem of resin-like residue. As shown in FIG. 2B, the photosensitive resin 52 is exposed to light and developed to thereby form at the bottom the apertures 53 through which the surface of the metal sheet 51 is exposed, but as shown in FIG. 5 of the accompanying drawings, undeveloped portions 56 may remain at the bottom of the apertures 53 in the photosensitive resin 52 and resin-like residue may remain in some cases. The presence of the undeveloped portions 56 is considered to be attributable to a case where the stagnancy of the developing liquid occurs and the development at the bottom becomes insufficient, or a case where the force of intimate contact between the photosensitive resin 52 and the metal sheet 51 is great and therefore it is difficult for development to take place, or a case where these two cases are compounded.
On the other hand, the occurrence of the resin-like residue becomes remarkable when the aspect ratio (film thickness/diameter of opening) of the apertures 53 is great, or when the exposure and developing conditions are inappropriate, or when diffracted light and/or reflected light irradiates the portions of the photosensitive resin which should not be exposed to the light. The presence of such resin-like residue has led to the problem that it hampers the exposure of the surface of the metal sheet 51 at the bottom of the apertures 53 and as shown in FIG. 5B, the shape of the recesses 54 is made irregular in the process of etching the surface of the metal sheet 51 and as shown in FIG. 5C, the shape of bumps is not constant and the electrical characteristic is not stable.
Also, in the gold plating step, there is the problem that the shape (e.g. diameter and amount of protrusion) of the gold bumps becomes non-uniform depending on the gold electroplating conditions, for example, the Reynolds number of liquid flow imparted to the plating liquid, the current density, the amount of a plating liquid additive etc.
Taking the current density distribution as an example, the amount of plating deposition is greater in the central portion than in the marginal portion under the influence of the current density distribution and therefore, in an electrical connecting member, the amount of protrusion of electrically conductive members present in the central portion becomes greater than the amount of protrusion of electrically conductive members present in the marginal portion and thus, it is not easy to make the diameter of protrusion and the height of protrusion of the electrically conductive members uniform. FIG. 6 of the accompanying drawings is a plan view of an electrical connecting member having four electrically conductive members 34, and FIG. 7 of the accompanying drawings is a plan view of an electrical connecting member having seven electrically conductive members 34. In the example shown in FIG. 6 wherein four electrically conductive members 34 are located at the verteces of a lozenge, the amount of protrusion of the two electrically conductive members 34 at the vertices the diagonal of which is shorter is greater than that of the other two electrically conductive members 34. Also, in the example shown in FIG. 7 wherein six electrically conductive members 34 are disposed so as to surround an electrically conductive member 34, the central one is greater in the amount of protrusion than the other six ones. Further, FIG. 8 of the accompanying drawings is a fragmentary plan view of an electrical connecting member 31 forming a pattern in which a number of rows of seven electrically conductive members 34 each are disposed. In each row, the amount of protrusion is smaller in the marginal portion than in the central portion. This is considered to be because the combined effect of the density of electric current is higher in the central portion than in the marginal portion. This leads to the problem that the bump deformation during the pressure joining of the electrical connecting member becomes great in a case where the amount of protrusion is great and this causes short-circuiting.
Also, it is necessary to make the shape of the formed gold protrusions constant so that bad connection may not occur in the above-described TAB, and various methods of forming gold protrusions of stable shape by gold plating have heretofore been proposed. These methods include, for example, a method of removing the ground metal layer just beneath the gold protrusions (Japanese Laid-Open Patent Application No. 61-141157), a method of leaving resist at the center of the opening portion (Japanese Laid-Open Patent Application No. 62-252951), a method of repeating the photolithography step and the gold plating step (Japanese Laid-Open Patent Application No. 63-175446), etc.
However, the forming methods as described above suffer from such problems as will be described below. In the method of removing the ground metal layer just beneath the gold protrusions, the removing step is cumbersome, and when the ground metal layer is removed in its liquid phase, etching liquid remains and this remaining liquid is liable to be mixed with the gold plating liquid to cause a bad shape. Also, in the method of leaving resist at the center of the opening portion, the area of contact with the ground metal layer is small and therefore the intimate contact property is deficient and thus, this method is liable to cause a reduction in the strength of the protrusions during boding. Further, the method of repeating the photolithography step and the gold plating method generally requires a long time as the steps, and the alignment in the photolithography step is difficult, and this leads to the problem that the control of the height of the gold plating in each step is difficult.